To protect electrical consumers against overloads a circuit supplying the electrical consumer or the electrical consumers must be able to be automatically interrupted. The interruption can be triggered in such cases for example on the basis of a heating-up associated with an overload, e.g. of a heating wire connected to the circuit, which enables circuit breakers with bimetal triggers to be used for example. Electronic solutions for overload protection are for example overload relays which typically comprise measurement transformers. These measurement transformers pass on to a processing unit a signal equivalent to the flow of current in a current path to be monitored; a heating up of the consumer is simulated on the basis of this signal. If the simulated temperature exceeds a pre-specified or prespecifiable value, an interruption of the current flow in the current path is triggered.
DE 195 32 197 describes the use of a current transformer for protecting against overload which comprises at least one primary and at least one secondary winding coupled to said primary winding in a transformational arrangement. For simultaneous precise detection of the rated current and of an overload a load in the secondary branch can be switched over from a first resistance value to a second resistance value, which prevents saturation during overload.
DE 102 53 018 discloses a switching device with at least one current sensor for detecting the current flowing through at least one current path. The switching device can also comprise at least one additional temperature sensor which measures and reports a temperature increase which is associated with a slow increase in the current in the case of an overcurrent, in order to be able to detect in the event of an error whether an overcurrent or a short-circuit current is present.